Marking of photographic film elements to provide, e.g., graphic elements, characters, bar codes or text is often desired in the photographic art. The showing of foreign language films in a motion picture theater, e.g., typically includes the simultaneous display of the translated dialogue in the form of marked subtitles. A current frequently used method of subtitle marking, described in U.S. Pat. Nos. 4,854,696 and 5,367,348, involves embossing or etching the subtitle text into the film's photographic emulsion image layer(s).
Marking is currently frequently done by laser ablation, wherein a laser beam of high energy travels along a determined path corresponding to the inscriptions to be formed on the film clement. In such method, the silver halide photographic emulsion present in the layer(s) coated onto the film support becomes ablated locally. Photographic color films comprise image dye-forming emulsion layers coated on a transparent support, and the marked or ablated areas comprise clear or low density areas surrounded by the unmarked dye-containing image areas. Similarly, for black and white films the marked or ablated areas comprise clear or low density areas surrounded by the unmarked image areas which contain silver metal. In the particular application of laser subtitling of photographic films, the quality of laser marked subtitles is dependent upon the density and color differences between the marks and the surrounding dye or silver image areas, and on the wavelength, power, and writing speed of the laser. The power and speed are selected to remove as much of image emulsion layers as possible without damaging or distorting the support. Laser subtitling is typically performed on the final color or black and white release print film intended for projection in a theater, but may also be performed on color intermediate or black and white films to form subtitle images which may then be optically printed onto another intermediate or black and white film to form a negative image, which may then be printed onto the final release print film.
Most laser subtitling systems were originally designed and optimized for marking motion picture films having acetate film base supports. A switch in the industry from acetate to polyester supports for motion picture print films has required the subtitlers to make changes in their operations to reoptimize results, which has been a problem as thermoplastic polymer support materials, such as polyester, are more succeptible to support damage. There is an inherent conflict between using sufficient power to mark in low density image areas without causing significant base damage in the high density image areas, as due to the non-uniform release of gelatinous residues or to the damage of the support, undesired dark and/or colored spots may be observed when the film image is enlarged and projected on the screen in a theater, especially for print films having polyester film supports.